Paraffin alkylation in the presence of hydrogen fluoride



Nov. 4, 1947. s T. HADDEN 2,430,333

PARAFPIN ALKYLATION In THE PnEsEns oF HYDROGEN 'FLuDE Filed June 22,1945 5 sheets-sheet 1 Nov. 4, 1947. s T. HADDEN v2,430,333

PARAFFIN ALKYLATION IN THE PRESENCE OF HYDROGEN FLUQRIDE Filed June 22.1945 5 Sheets-Sheet 2 @ya Jy. .3.

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PARAFFIN ALKYLATION JN `THE PRESENCE OF HYDROGEN FLUORIDE Filed June 22,1945 3 Sheets-Sheet 5 .fa ATTO NEY Patented Nov. 1947] v. V

PARAFFIN ALnYLArIoN 1N THE PRESENCE `or HrDnoGEN rLUonmE Stuart T.Hadden, Woodbury, N. J., asslgnor to y Socony-Vacuum Oil Company,Incorporated, a corporation of New York Application June 22, 1945,Serial No. 600,873

This invention relates to a process for the catalytic alkylation of lowboiling isoparaillns by reaction with low boiling olens in the presenceof liquid hydrogen nuoride. More specically, the invention contemplatesconducting said alkylation reaction on trays of no1/e1 design inapparatus of the general nature of a fractionating column.

As now practiced commercially, hydrogen fluoride alkylation of isobutanewith butenes and the like employs a contactor of expensive design toeffect the reaction. An emulsion of liquid hydrogen fluoride and liquidhydrocarbons including both reactants and reaction products iscirculated Within the contacter to provide a contact time on the orderci 1l) to l5 minutes or greater. Since the reaction is exothermic, heatof reaction must be abstracted to maintain the desired reactiontemperature. This is accomplished by means of indirect heat'exchangeelements in the contactor. Indirect heat exchange of this type isnotoriously inefcient and the requirements of the unit for coolingmedium and agitation are very large. A portion of the circulatingemulsion is continuously withdrawn from the contactor andpassed to asettler, being replaced by fresh reactants and acid catalyst. Acid settled out in the settler is recycled to the contactor, at least aportion being passed through equipment for regeneration by removalV ofwater and accumulated heavy polymers.

The hydrocarbon layer is transferred to elaborate fractionatingequipment for preparing the product for use as aviation fuel. Oneelement of this fractionating setup is an isobutane column to yieldrelatively pure isobutane for recycling to the reactor. The highproportion of isobutane to olefin in the charge to the contactar(normally 5 to 1 or greater) places a heavy load -on the isobutanecolumn for recovery of unreacted isobutane to be reused in the process.Since a high reflux ratio prevails inthis column, its construction andoperating cost are very sizeable items in,

combination of functions not only eliminatesI equipment heretoforebelieved necessary, but ln addition I am able to employ a novel methodof abstracting heat of reaction by cooling means in the nature ofcondensers at a point remote from 6 Claims. (Cl. 260 -683.4)

the actual reaction zone.4 The removal of heat by condensation ofvapors-is vastly more efficient than indirect heat transfer to cool aliquid phase, it being possible to use smaller equipment and to utilizemore fully the available cooling eiect of plant cooling water.

A further highly important advantage of the invention lies in the factthat by use of the present invention, alkylation is carried out at apoint atewhichthere is inherently a very high proportion ofisoparailins, a condition favorable to alkylation in that it tends tosuppress undesirable side reactions such as polymerization.

In its preferred embodiments, my invention also contemplatesincorporation of an acid settler and an acid stripper in the sameapparatus as the reactor and deisobutanizer, still without greatlyincreasing its original or operating costs above that of presently-usedisobutane columns. My invention also permits-because of its simple andefficient temperature control featuresutilization of the advantagesaccruing from introduction of the reactant charge at temperatures abovethe rereactants as described and claimed in application Serial No.481,430, iiled April 1, 1943, by I-Iarry Gr. Doherty and Arlie A.OKelly. It will be readily seen that either of the'se expedientsgreatlyincreases the heat transfer load imposed on the system, yet the`increased cooling is readily accomplished according to my invention.

In essence the invention contemplates conducting the reaction on bubbletrays of novel design and refluxlng vapors from the reaction trays toprovide cooling of the actual reaction zone by direct contact ofreactants and catalyst with cool liquid consisting of hydrocarbons andcatalyst. The novel bubble trays of this invention include a fresh feed.inlet, and are arranged for balliing vapors fromthe next lower tray tobe mixed with the fresh feed in a zone isolated from the liquid of thelower tray and thus act to inhibit contact between fresh feed for areaction tray and the liquid of the next lower tray, Whether the latterbe also a reaction tray or a tray of more conventional function vbelowthe reaction section. When such contact is permitted, either with thebody of liquid on a vtray or the liquid spray thereabove, there is atendency to dissolve olens of the feed in condensed hydrocarbons, whichhave been depleted of olens by alkylation.' Solution of olens in thecondensed hydrocarbons is unn desirable because the contacting ofliquids is less intimate than that of vapors, hence-liquid phasealkylation does not favor high quality product.

The objects and advantages of the invention will be more clearlyunderstood from the description below of preferred embodiments of theinvention, apparatus for which is shown inA the annexed drawings,wherein:

Figure 1 is a diagrammatic representation of apparatus for practicingthe invention;

Figure 2y isa sectional elevation of part of the reactionsection showingtwo designs of reaction trays for accomplishing the purposes of theinvention;

Figure 3 is a view similar to that of Figure 2, showing a different typeof trays for the reaction section;

Figure 4 is a plan view of a preferred embodiment of reaction traydesign; y

Figure 5 is a section on line 5-5 of Figure 4;

Figure 6 is a plan view of a vapor injector for the tray of Figures 4and 5; and

Figure '7 is a section on line 'I-'I of Figure 6.

As shown in Figure 1, the principal apparatus element employed inpractice of the invention is a bubble tower III, preferably of at leastfifty plates. Of these plates, the upper section-say, three to tenplates-functions as a rectifying sec.= tion and the bottom section-say,about thirty or more plates-acts as stripper. Between the rectifyingsection and the stripping section is a reaction section, which mayadvantageously include about one to five plates or more if theparticular conditions of operation warrant. This arrangement is verysimple in construction and Operation, since control of conditions in thereaction section is accomplished by adjustment of a relatively fewelements of high thermal efilciency external to the actual zone ofreaction. Thus, cooling of the reaction zone is accomplished byisobutane reflux, the heat being actually abstracted from the system bya condenser instead of the much less eicient cooling coils employed inpresently used liquid phase apparatus. Heat is derived, if needed, fromthe stripping section by rising vapors which condense in the reactionzone. As the description proceeds it will be clearly seen how heatexchange in the process of this invention is accomplished largely, ifnot solely, by condensation and evaporation; steps capable of handlinghigh heat loads simply and efficiently.

Taking as a typical example the reaction of isobutane with butenes inthe presence of hydrogen iiuoride to produce a product suitable for usein aviation gasoline, a fresh charge containing isobutane rand butenesis supplied in the vapor phase,

preferably superheated, to the vapor space below the trays in thereaction section by manifold II and inlets I2. Superheating isadvantageous in that it prevents any condensation of vapors rising fromthe plate below and the consequent solution of olens from the feed bythe droplets so formed, the same being carried to the plate below.Super.- heating is particularly desirable for installations where thetrap tray is designed so that no vaporization occurs thereon becauseunder these circumstances there is a temperature drop of about 30 F.from the top stripping tray to the lowest reaction tray.

On the reaction trays is a body of liquid through which passes ar vapormixture admitted by the bubble caps or orifices on the trays. very highratio of isobutane tobutenesris maintained on the trays by reason of-the isobutane reilux"from` the rectlfying section thereabove. Hydrogenfluoride in liquid phase is supplied from manifold I3'by inlets Iland/or spray head I 5. Thishydrogen fluoride and the isobutane recyclealso serveto cool the reaction section by removing heat f reaction aswell as heat of condensation of vapor phase reactants and/or sensibleheat of preheated reactants. The said cooling is accom- Aplished byevaporation of isobutane and hydrogen fluoride, the resulting vaporspassing up into the rectifying section and out the top of the columnwhere they are condensed ln condenser I6 and collected in decantingaccumulator 28. The hydrogen fluoride layer is returned to the reactionzone through manifold I3 while the isobutane layer is returned to thecolumn normally as reflux through line I8. Part of the isobutane layermay be returned as recycle feed through line I8. Introduction of theisobutane layer as reux serves to effect the desired rectification,provides the desired concentration of this reactant in the re` actionzone and removes the heat of reaction from the tower. Return of theisobutane as recycle feed'serves to provide the desired proportion ofthis reactant in the reaction zone without increasing the load on thereboiler. Provision for these alternate methods of returning theisobutane layer to the tower thus increases the flexibility of theprocess.

An important advantage of the present invention lies in the simplicityof control of process variables and the flexibility of the process inthat respect. The ratio of hydrocarbons to catalyst and the effectiveresidence time, i. e., the period during which hydrocarbon reactants arein contact with acid catalyst may be effectively controlled by the feedrates and the height of dams on the` bubble trays. The feed rate of anygiven substanceincludes not only the fresh material introduced by themanifolds II and I3 but also liquids from the -rectifying section andvapors from the stripping section. The residence time on any givenreaction plate may be held to a few seconds by the controls mentionedabove. If very short residence times are desired, a trap-out tray may beinserted between each two adjacent reaction plates and the residencetime thus held to the time for one plate. Such trap trays may beexternal to the column in order to avoid introduction of hydrogenfluoride vapor to the reaction trays.

An unusual feature of the present invention is that it provides forseveral points of contact between acid and hydrocarbons in a systemwhere the general ow of hydrocarbons and acid is concurrent. It will benoted that vapors of isobutane and such lighter hydrocarbons as may bein the feed or formed as by-products will rise from tray to tray.Even'here there is a concurrent flow of hydrogen fluoride. Some alkylatecomponents also probably are carried up with the vapor, but the neteffect is to pass the predominant portion of alkylate together with amajor portion of the hydrogen fluoride downwardly as liquid to a trapouttray 2l on which the mixture separates into an acid phase withdrawn at22 for recycling, with or without regeneration in a conventional unit23, and a hydrocarbon fraction passed downward to the stripping section.As noted above, the trap tray 2| may be external to the column in orderto reduce or eliminate hydrogen fluoride vapors in the vapor risingtothe reaction tray. As the alkylation product, containing n-butane andhigher boiling hydrocarbons passes through the stripper section,dissolved hydrogen fiuoride, isobutane and other light hydrocarbons areremoved and returned as vapor to the reaction section. Heat to operatethe stripping section is supplied by reboiler 24 which also functions,when desirable, to supply heat by rising vapors from the bottom sec tionto the reaction section.

I'he alkylate product is passed to fractionationA Referring to the flowsheet in greater detail? fresh charge, for example, a butene-butanemixture supplied by line I1 admixed if desired with recycled isobutanefrom isobutane recycle line I8, is passed through a heater I9, fromwhich heated vaporous charge passes to manifold Il. Each of the inletsI2 admits charge vapor to the vapor space below a reaction tray in thereaction section of the tower where the charge mixes with vapors risingin the towerA and passes through bubble caps or orifices on the reactiontray to agitate. V.lit the same time, hydrogen fluoride in liquid phase.is admitted to the reaction trays from manifold I3. This hydrogenfluoride, together with liquid hydrogen fluoride owing to each tray fromabove, serves to catalyze the alkylation reaction. On each tray thereisa separation of vapor and liquid, the latter spilling over the dam asa mixture of acid, alkylate and light hydrocarbons to pass to the nextlower tray. Vapors passing upwardly will comprise isobutane, normalbutane, acid vapor and a minor quantity of alkylate.

The liquid phase mixture of acid and alkylate passing down through thereaction section will contain lighter hydrocarbons such as isobutanebecause the separation in the reaction section is not sharp. Normalbutane will also exist in both phases but the tower is preferably sooperated that a major portion of the normal butanein the system iswithdrawn with the alkylate. The liquid phase from the lowermostreaction tray passes to trap-out tray 2|, within the column .or externalthereto or. which it is maintained relatively quiet and straties toproduce a lower acid layer which is withdrawn by pump 20 and an upperhydrocarbon layer which passes by downcomer 2B to the stripping section.In the stripping section, acid and isobutane will be largely removedfrom the alkylate which is then transferred to a column 21 in whichlight constituents, e. g. butane and such isobutane as may re- 'main inthe alkylate, .are separated from the alkylate product.

The acid layer discharged from pump 20 is recycled to the manifold I3 ordiverted to acid regeneration unit 23 from which purified catalyst isreturnedto the system. Preferably a. portion of the discharge of pump 20is continuously diverted for regeneration.

The overhead from tower I0 is condensed in condenser i6 and transferredto a settler 28. The upper, hydrocarbon layer furnishes reflux for therectifying section of tower Ill and the lower layer is withdrawn andrecycled to acid feed manifold I3. A portion of the upper layer fromsettler 28 may be recycled through line I8 to fresh feed line I1 andanother portion is sent to stripping column 29 wherein dissolved acidisremoved and recycled to the alkyiation zoneof tower III. Bottoms from'stripper 29 are transferred to depropanizer 25 for removal of propaneand the remaining isobutane may be returned to the system as recycle tofeed or reflux to tower I0. If circumstances warrant, bottoms fromstripper 29 or depropanizer 25 or both may be diverted in whole or partto the alkylate stream to debutanizer 21.

In a typical operation, charging isobutane and butene to produce motorfuel and aviation alkylate. the tower is operated at 103 pounds persquare inch gauge and atemperature of l21 F. in the reaction section.The ratio of isobutane to butenes in the reaction section is aP-proximately six to one when the top tray of the tower is at 108 F.(condenser temperature, 100 F.) and the bottom tray at 182 F. y(reboiler 241 F.). .The feed `vapor is preheated -to F. before chargingto the reaction section.

This general scheme of `allrylation is that described in the applicationof Thomas P. Simpson referred to above. According to the present in-.

y vention, operation of the process is improved by the use of plates ofnovel design which effectively baille vapors passing upwardly from trayto tray with addition of fresh charge to vapor substantially free ofspray and introduction of the vaporous mixture to the next higherreaction tray. By this means, I avoid the abstraction of olefins fromthe vapor phase charge by solution in drops of spray which would cause apart of the olefin to be subjected to liquid phase alkylation uponfalling back into the lower tray.

In Figure 2, the reaction section includes trays for retaining a fairlydeep body of liquid, say ten to twelve inches or more in depth, withprovision for introducing vapor phase feed through small holes in thebottom of the tray. The tray is made up of a vessel 3l havingperforations in the bottom as shown and supported from the walls of thecolumn by webs 32 and 33 which also serve as the bottoms of troughsdefined by downflow weir 34 and overflow weir 35. Spaced about thevessel 3| is cup-shapcdbaffle 36 into which fresh feed is introduced tobe mixed with vapors substantially free of spray from the next lowertray. f

Liquid flow from tray to tray downward in the reaction section isaccomplished by means of downcomers 31 which are of such length that thehydrostatic head of liquid therein is greater than the pressure drop ofvapors between adjacent trays.

The two trays shown in Figure 2 differ in th manner in which thevaporous fresh feed is introduced. In the case of the upper tray, aperforated circular pipe 38 supplies feed from a feed line 39 to thespace between the vessel 3| and the baille 36. This fresh feed mingleswith vapors free of spray from the next lower tray and the mixture isintroduced to the acid catalyst through the perforations in the bottomof vessel 3l.' In order that the apparatus may be readily drained ofacid catalyst when shut down, weep holes 48 are provided at points wherebodies of acid might =`be held up.

The lower tray of Figure 2 is arranged for ntroduction of fresh feedfrom line 39 to the bottorn of cup-shaped baille 36. In order to insureadequate mixing of fresh feed with vapors from the next lower tray,baffles 4I are interposed below the perforated bottom of vessel 3l. Uponshutting the unit down, acid may be drained from the bottom of baille 36by opening valve 42.

Turning now to Figure 3, the invention may be practiced on plates ofmore conventionall design,`

having b bble caps which diifer from those normally us in fractionationequipment in their height. The bubblecaps 43 are made high to permit ofthe use of tall chimneys 44 coacting with the plate 46 to baie vaporsrising from the next lower plate to inhibit carry, ,ov.er of liquidspray to the point of fresh feed introduction. The fresh feed issupplied by tubes 46 projecting well into chimneys 44 from line Il. Thusthe possibility of liquid hydrocarbons dissolving olefins from the feedto drop back to the lower tray and be alkylated in liquid phase isavoided. An overflow weir 41 and a web 48 form a trough for supply ofliquid to downcomer 31, the bottom of which empties into a baille 4B toprevent entry of vapors from the lower tray into the downcomer. As inFigure 2, weep holes 40 are provided to permit drainage of acid when theunit is shut down.

The alkylation reaction occurring under conditions described above,namely bubbling vapor phase charge up through a body of acid catalyst,proceeds better if the charge includes an excess of the isoparafiinreactant. Normally, I prefer to operate with an excess of that reactantin the fresh feed introduced, but that excess need not be great, sincethe mixing of fresh feed with vapors from the lower tray according to myinvention will give a reasonably uniform charge mixture in which theisoparaflln is present in large excess. The acid bodies employed on thetrays should be quite deep compared with usual fractionating practice,said ten to twelve inches or more.

A particularly advantageous iorm of reaction tray is shown inFigures 4to7, inclusive, which comprises a high chimney supplying vapors for anorifice plate. As shown, the plate is made to rest on a flange in thecolumn. A metal gasket ring 50 is affixed to the periphery of a plate 5|through which passes a downcomer 52 and a chimney 53. A cap 54, orificeplate 55 and circular wall 58 define a vapor space above the plate Iland about the chimney 53 from which the vapor phase alkylation charge isintroduced by injectors 51 to the deep body of catalyst on the tray. l

The said injectors 5l are preferably formed to provide a number oforifices each and are threaded as shown to engage tapped holes in theorifice plate 55. Vapors from below the orifice plate 55 enter a centralbore 58 in each of the injectors and are passed by a plurality (seven inthe form shown) of orifices 59 into the body of catalyst.

I claim:

1. In a process for the catalytic alkylation of isoparafllns by reactionwith oleflns in the presence of liquid hydrogen fluoride in afractionating column by introducing a fresh feed of isoparaifins andolefins below at least one tray in a reaction section of said columnintermediate the upper and lower trays thereof, refluxing vapors fromsaid reaction section in a reiiuxing section of said column above saidreaction section and returning reflux liquid therefrom to said reactionsection, stripping liquid from said reaction section in a strippingsection of said column below said reaction section and returning vaporstherefrom to said reaction section; the improvement which comprisesbaffling vapors rising in the column immediately below each tray in thereaction section to disengage liquid spray from the next lower tray,mixing fresh feed with the said bailied vapors to thereby produce asubstantially uniform acsqase reaction zone, introducing vapors of saidisopara'fiins and said oleflns to the lower part of said body,

' maintaining conditions of temperature and pressure in saidreactionzone such that alkylation products will be predominantly liquidand unrev acted isoparaiiins will be evaporated from said body togetherwith a portion of said hydrogen nuoride, reiluxing vapors from said bodyand returning liquid from said reuxing to said body to cool the same,return evaporated hydrogen fluoride and maintain a high ratio ofisoparafilns to olens in said zone, continuously withdrawing liquid fromsaid body, settling said withdrawn liquid to produce an acid phase and ahydrocarbon phase, returning hydrogen fluoride from said acid phase tosaid body, fractionally distilllng said hydrocarbon phase to produce avapor therefrom containing hydrogen uoride and light hydrocarbons andintroducing said vapor to said body with said vapors of isoparafilns andolefins; the improvement which comprises baiing said vapor from saidhydrocarbon phase to disengage liquid spray, mixing fresh feedcontaining isoparafllns and olefins therewith and introducing theresultant mixture to said body as aforesaid.

4. In a process for alkylation of vaporized isoparafiins with vaporizedoleflns by maintaining a plurality of shallow superposed bodies ofliquid hydrogen fluoride within a reaction zone, introducing vapors ofsaid isoparamns and said olens to each of said bodies, maintainingconditions of temperature and pressure in said reaction zone such thatalkylation products will be predominantly liquid and unreactedisoparamns will be evaporated Ifrom each of said bodies together with aportion of said hydrogen uoride, introducing vapor from each of saidbodies below the uppermost to the body next thereabove with said vaporsof isoparaffins and oleiins, continuously withdrawing vliquid from eachof said bodies above the lowermost and passing said liquid to the bodynext therebelow, refluxing vapors from said uppermost body and'returning liquid from said refluxing to said uppermost body to cool thesame, return evaporated hydrogen fluoride and maintain a high ratio ofisoparaiiins to olens in said uppermost body, whereby similaradvantageous results are achieved in bodies therebelow by reason ofliquid passed downwardly as aforesaid, continuously withdrawing liquidfrom said lowermost body, settling liquid so withdrawn to produce anacid phase and a hydrocarbon phase, returning hydrogen fluoride fromsaid acid phase to said bodies, fractionally distilling said hydrocarbonphase to produce a vapor therefrom containing hydrogen fluoride andlight hydrocarbons and introducing said vapor to said lowermost bodywith said vapors of isoparafiins and oleflns; the improvement whichcomprises baiiiing said vapor from said hydrocarbon phase to dlsengageliquid spray, mixing fresh feed containing isoparamns and olefinstherewith and introducing the resultant mixture to said body asaforesaid.

feed mixture and introducing said feed mixture to a body of acid on saidtray as a vapor sub- 5. A method of operating a bubble tower to conducttherein an alkylation reaction between isobutane and butenes in thepresence of liquid hydrogen fluoride on reaction trays betweenrectifying trays in the upper portion and stripper trays in the lowerportion of said tower, comprising maintaining said reaction trays atconditions of temperature and pressure to maintain hydro-i carbons ofhigher boiling point than isobutane substantially in the liquid phaseand to evaporate isobutane, baiiilng vapors rising in the towerimmediately below each of said reaction trays. mixing the baiiied*vapors with isobutane and butenes, injecting the resultant mixture intothe acid on each of said reactionA trays, supplying liquid hydrogenfluoride to said reaction trays, removing isobutane vapor` from abovesaid rectifying trays, condensing at least a. portion of said isobutaneandreturning the condensed isobutane to said rectifying trays as reiiux,settling liquid at a point in said tower between said reaction trays andsaid stripper trays to form an acid layer and a hydrocarbon layer,recycling said acid layer to said reaction trays, passing saidhydrocarbon layer downward to said stripper trays, withdrawingcondensate from below said stripper trays, evaporating a portion of saidcondensate, 'and returning a portionof said vapors to stripper trays inthe lower part of said tower.

6, The process of claim 1, characterized in that said isoparafiin isisobutane and said olens are butenes. 4

STUART T. HADDEN.

REFERENCES CITED 'The following references are of record in the iilc ofthis patent:

UNITED STATES PATENTS

